The present invention relates to a method and apparatus for determining the position of peripheral points of bodies, especially of bodies of rotation, relative to an axis of the body.
In the case of large bodies, especially of bodies of rotation, it is oftentimes necessary to locate certain points or sectional areas of the surface of the body at a specific distance from an axis or to determine the distance of the points or areas from the axis of the body.
Conventional measuring systems can be used for this purpose and include for example machines for measuring co-ordinates and parallel surface gauges used in conjunction with lathes or plane tables having an apparatus to rotate the body to be measured.
If such measurements require a certain degree of accuracy, the known measuring systems must be operated with great care which consumes a relatively great amount of time. Furthermore, the accuracy of the measurement will depend to a large extent on the skill of the individual operator.
The last-mentioned factor will be particularly important if several points or sectional areas of the body at an equal distance from the reference axis are to be measured and if the gauge must be reset for each individual point due to the shape of the body.
A practical example of a body which is measured in this way includes a turbine rotor that is equipped with buckets arranged in a bucket ring. Due to inaccuracies occurring during manufacture and assembly, peripheral points of the installed buckets will be at non-uniform distances from the axis of rotation. Such an arrangement would result in non-uniform radial clearances between the bucket ring and an inner housing wall after installation. A minimum radial clearance is desirable, however, so as to attain a maximum degree of efficiency. The minimal clearance has been accomplished heretofore by inserting the rotor into a lower housing part and by filing each individual bucket radially until the desired clearance has been reached. The other blades of the turbine rotor are then machined down to the size of the reference blades of the buckets. This method is tedious and time-consuming and must often be repeated until the clearances meet the required tolerances.
In order to minimize the expense and the processing time connected with the known methods of the prior art an attempt was made to find a way to machine turbine rotors equipped with blade rings to a finished size independently of the housing. For this purpose a rotor-finishing bench was provided which required an apparatus to measure the peripheral extent of the bucket points. Such an apparatus had to meet the above-stated requirement for a quick and problem-free operation which provides both uniform and precise measuring results. Another requirement was that the device provide objective instrumentation, thus eliminating inaccuracies resulting from the actions of the operator. These inaccuracies may result for example from non-uniform pressure by the operator in applying the known measuring devices to the body to be measured.
Accordingly, it is an object of the present invention to provide a measurement method and device which overcomes the disadvantages of the known prior art.
Another object of the present invention is to provide a measurement device having an electrical contact indication feature.
The apparatus proposed by the present invention includes two carriages which can be moved in two directions perpendicularly with respect to each other. A sensing gauge head is fastened to the upper carriage by means of a cantilever arm. The sensing gauge head includes a measuring wire which is under mechanical stress forming one portion of an electric circuit. The circuit is wired in such a manner that the circuit will close when the measuring wire comes in contact with the body to be measured. The circuit includes an indicating device which services to indicate the contact of the measuring wire with the body to be measured. A low voltage current source is provided to energize the circuit.